/* slider about */
.slider{
    width: 280px; 
    height:10px; 
    margin:10px 0;
    position: relative
}
.background-line{
    position:absolute;
    height: 1px;
    width:100%;
    top:4px;
    left: 0;
    background-color: #000
}
.bar {
    width:10px; 
    height:10px;  
    background-color:#000;
    border-radius: 10px;
}
.bar:after {
    content: "after";
    width: 40px;
    height: 40px;
    position: absolute;
    top: -15px;
    left: -15px;
    opacity: 0;
    background-color: yellow;
    color: red;
    font-weight: bold;
}